1. Field of the Invention
This invention relates to external preparations with improved stability against discoloration comprising kojic acid purified by sublimation.
2. Description of the Prior Art
Kojic acid is known as a substance capable of effectivity inhibiting the formation of melanin in the human skin.
Cosmetics have also been disclosed which utilize the melanogenesis inhibitory action of this acid (for example, Japanese Patent Kokai No. 53-3538, and Japanese Patent Publication No. 56-18569, No. 61 109705, No. 62-3820).
Also known are external preparations utilizing the melanogenesis-inhibitory, anti-inflammatory and analgesic actions of kojic acid (for example, Japanese Patent Publication No. 61-10447, No. 58-3446, No. 60-27648, and Japanese Patent Kokai No. 61-143313, No. 61-143314).
Kojic acid contained in these cosmetics and external preparations has been accepted as an excellent ingredient capable of inhibiting the formation of melanin with no side effect to the skin.
However, the external preparations containing kojic acid tend to become discolored with the passage of time, thus lowering their commodity value, unless careful considerations are given to the removal of metal ions from the water, materials and equipment used for the manufacture thereof, the pH of final products and other factors.